In the process of testing sandwiches, Russo discovered a new favorite, the Pork Tenderloin Sandwich, also called “The Iowa Skinny.” She describes it as “a monstrous breaded, fried slab of pork tenderloin that completely overwhelms a hamburger bun and is simply dressed with mayo, onions and pickles.”

After four intense months, she found she had grown weary of eating sandwiches and also had gained 7 pounds.

In her research, Russo says she discovered that interest in sandwiches has “exploded” in the last couple of years. “Looking at Los Angeles, New York and San Francisco, there are a lot of new restaurants — bona fide restaurants — serving only sandwiches,” Russo says. “At XOCO, a Rick Bayless restaurant in Chicago, they serve the most amazing tortas I’ve ever had. And some restaurants serve only one kind of sandwich!”

The variations are endless, according to Russo. “New sandwiches are popping up all the time.” She believes a lot of the current experimentation has to do with the high quality and variety of breads and other sandwich staples.

“Nowadays we have so many artisanal breads,” says Russo. “You can find anything — sweet breads, olive oil and rosemary, dill and Cheddar. … Plus all kinds of sauces and cheeses.”

And social media plays a role, too. “People are always posting ideas on Facebook and Twitter,” she says. “The Wikipedia page on sandwiches is constantly being updated.”

Bottom line, Russo believes the continuing appeal of sandwiches has a lot to do with form and function.

“Historically, they have been a food of convenience, because you could eat and do something else at the same time,” she says. “And cold cuts made life so much easier; you didn’t have to depend on having leftovers anymore.”

In her own life, Russo and her husband, who live downtown, have their own sandwich ritual.

“It’s definitely part of our diet,” she says. “One of our traditions is frittata sandwiches on Sunday mornings.”